Availability of efficient starters is one of the most important elements during fermentation technology. Acetic acid bacteria (AAB) face extreme conditions (low pH, high acetic acid concentration (>7%), ethanol and high temperature) during vinegar fermentation. In spite of introduction of broth media contained viable AAB as starter by some companies; traditional methods for initiation of vinegar fermentation are still used even in modern factories, therefore there is a long Lag phase for initiation of fermentation. In recent studies in CWBI, a kind of lyophilized starter has been produced by using an isolated thermotolerant bacterium: Acetobacter senegalensis. The aim of this study is to determine the best media for revitalization and the optimum temperature for preservation of the freeze-dried cells. To produce biomass, glucose was used as carbon source in batch culture under regulated conditions. The cells harvested when they reached to stationary phase. Harvested cells suspended in spent growth medium (final supernatant of fermentation). Maltodextrin (10%), manitol (20%) and spent growth medium were used as protestants. After freeze-drying they were subjected to storage test at -20° C, 4° C and 35° C for six months. The viability of cells determined by using spread plate technique using three different media: YG (yeast extract, glucose) and YGE (yeast extract, glucose, ethanol) and YGEA (yeast extract, glucose, ethanol, acetic acid). According to residual viable cells, manitol and maltodextrin showed higher protective functions rather than spent growth medium (92.3%, 88.2% and 82.1% survival, respectively) during freeze-drying process. Viability of cells during rehydration is completely dependent to the composition of the broth media used for this purpose. Adding ethanol (>0.5%) or acetic acid (>1%) to rehydration medium caused 40-45% reduction in viable cell numbers in comparison to YG broth. The composition of culture media can also influence the growth of bacteria after rehydration. In YG, much higher cell growth (about 1 log unit) was observed in comparison to YGE and YGEA. Addition of glucose (20 g/l) to YGE can neutralize the adverse effect of ethanol considerably but it cannot improve the growth in YGEA. This can be partially explained according to the activity of alcohol dehydrogenase and acetaldehyde dehydrogenase. It was revealed that freeze-dried cells had very low activities for these two enzymes. Analysis of total soluble protein contents of lyophilized cells during storage at different conditions revealed that the soluble protein content of cells reduced by increasing the storage temperature. At 35° C after 15 days, there were 4.87 log units reduction in the viability of cells, and also about 14% less soluble protein was detectable under this condition whereas keeping of cells at -20 or + 4° C had no influences on protein and viability of cells. Storage of cells at +4° C in darkness for six month showed that about 79.2% and 68.3% viability of cells remained for cells protected by manitol and maltodextrin, respectively. To assess the real activity of lyophilized cells as starters, they were introduced to broth media (YGE contained 20g/l of glucose). It was seen that 6 months old lyophilized cells (with maltodextrin or manitol as protectants) were able to grow and consume 5 v/v of ethanol in 48 hr in the presence of initial acetic acid concentration (0.5%) at 30° C. In conclusion, the mentioned methods for preservation and reactivation of freeze-dried Acetobacter senegalensis can provide a promising tool for decreasing the lag phase of vinegar fermentation. [less ▲]

In this work, moulds growth was monitored during malting of a red sorghum from D.R. of Congo. Results obtained with chemical treatments [diluted alkalines: NaOH 0.2% (T1) and Ca(OH)2 0.1% (T2)] were ... [more ▼]

In this work, moulds growth was monitored during malting of a red sorghum from D.R. of Congo. Results obtained with chemical treatments [diluted alkalines: NaOH 0.2% (T1) and Ca(OH)2 0.1% (T2)] were compared with those of biocontrols [use of Bacillus subtilis S499 108 cells / mL: supernatant + cells (T3), cells (T4) and cells-free supernatant (T5)]. Chemical treatments have shown the highest fungal contamination levels, the highest malting loss, but better enzyme activities (α and β-amylases, limit-dextrinase, α-glucosidase and β-glucanase). The inhibition tests showed that the concentration of lipopeptides is correlated with the reduction of moulds growth. Malting trials with starters of Bacillus subtilis S499 showed that culture dilution affects the growth of moulds during red sorghum malting. The combination of a chemical treatment such as diluted NaOH with a biocontrol could be used to improve sorghum malts quality in terms of different enzymes activities and by reducing the level of fungal contamination. Key words: Bacillus subtilis S499, mould, sorghum malting [less ▲]

In order to produce hydrogen at high yields and production rates, the biotechnological process needs to be further optimized and efficient bioreactors must be designed. A biodisc bioreactor has been ... [more ▼]

In order to produce hydrogen at high yields and production rates, the biotechnological process needs to be further optimized and efficient bioreactors must be designed. A biodisc bioreactor has been design and investigated to produce biohydrogen from glucose by the Clostridium butyricum CWBI1009 strain at a high yield and production rate. This reactor, working continuously, has an internal volume of 2.3l but a working volume (liquid phase) of 300ml. Firstly, it enhances the hydrogen production rate (by about 3 times more than a completely stirred bioreactor) by partially fixing the bacteria on the porous support and thus increasing the cell concentration in the bioreactor (decoupling of HRT and SRT). Secondly, the rotating biodisc design enables efficient gas transfer (hydrogen and carbon dioxyde) from the liquid phase where it is produced by the bacteria to the headspace. Indeed, this is an important way to increase hydrogen production yields (by about 25% compared to a completely stirred bioreactor) by allowing the bacteria to focus on the metabolites pathways that produce more hydrogen. Other reactors designs have shown such good results by increasing the interfacial surface. [less ▲]

Termites gut may overcome important dietary perturbations, initial diversity acting as key point buffering effects on host, although termites possess their own enzymatic system. Some artificial diets ... [more ▼]

Termites gut may overcome important dietary perturbations, initial diversity acting as key point buffering effects on host, although termites possess their own enzymatic system. Some artificial diets permitted a simplification of the lower termites gut symbiotic system, which could be used as first step in symbionts isolation and cultivation. Preliminary assay of cultivation actually gave encouraging results. Proteomic proved to be suitable tool to investigate such a complex system. Nevertheless, for some symbionts very few genes are sequenced, which should lead to more targeted proteomic studies. Protein chromatography will allow to split up the proteome and more accurate analysis. [less ▲]

The dynamics of microbial stress response in intensive cultivation conditions remains misunderstood. In this work, two green fluorescent protein (GFP) transcriptional reporters have been used as ... [more ▼]

The dynamics of microbial stress response in intensive cultivation conditions remains misunderstood. In this work, two green fluorescent protein (GFP) transcriptional reporters have been used as biosensors of the heterogeneities generated in a two-compartment scale-down reactor. The stress promoters have been chosen for their responsiveness to carbon limitation corresponding to the global substrate profiles encountered in intensive fed-batch cultures. From our results, it can be concluded that the exposure of microbial cells to substrates heterogeneities tends to decrease the GFP expression level in fed-batch mode. Fluorescence intensities have been monitored at the single cell level by using flow cytometry. During the course of the fed-batch culture, a drop at the level of the intracellular GFP content has been observed for the two scale-down operating conditions and for the two promoters sensitive to substrate limitation (rpoS and csiE). The fluorescence drop can be attributed to the repression of these promoters but also to the release of GFP to the extracellular medium according to the increase of the fluorescence level of the supernatant. This leakage has been observed for all the operating conditions, i.e. the scale-down reactors and the culture operating in the normal mode. Interestingly, GFP leakage is more pronounced in the case of the cultures operated in the normal mode. Indeed, staining by propidium iodide (PI) tends to be more elevated for the microbial cells cultured under the normal mode by comparison with those cultured in scale-down conditions, indicating a higher permeability of the membrane. These results are in accordance with previously published ones (Hewitt and co-workers) suggesting that microbial cells cultivated in heterogeneous bioreactors (scale-down and large-scale bioreactors) exhibits a higher viability level. These results suggest that GFP microbial biosensors could be used to detect simultaneously mixing imperfections and their impact on the viability of microorganisms. [less ▲]

The project MICRO-H2 aims to study and exploit the microbial (bacterial and algal) production of hydrogen (H2). In addition to building a competence centre around the H2 production by microorganisms and ... [more ▼]

The project MICRO-H2 aims to study and exploit the microbial (bacterial and algal) production of hydrogen (H2). In addition to building a competence centre around the H2 production by microorganisms and the molecular monitoring of the processes, this project tries to address two main socio-economic issues. First, transport and many economic activities will be based on hydrogen energy in the near future. Secondly, many researches and technology developments deal with renewable resources. Therefore, a new integrated technology for a sustainable development should be promoted. Photofermentation and dark-fermentation are the most promising ways to produce biohydrogen. The main advantage of the first process is the complete conversion of substrate, if any, to hydrogen. However, present H2-production rates by microalgae remain low. Therefore, a better understanding of the microalgal hydrogen metabolism and rate improvements by genetic engineering are needed. On the other hand, dark-fermentation achieves at present far higher H2-production rates, but improvements are expected through monitoring and optimisation of bacterial diversity and activity. The objectives about bacterial H2 production were to increase knowledge, stability potentialities and investigation skills about the consortia of bacteria involved in bioreactors treating wastewater rich in carbohydrates to produce biohydrogen. The project focused mainly on the study of the potentialities of different consortia, with a focus on Clostridium strains. Concerning the microalgal production of H2, the objectives were to increase knowledge on the metabolic interactions that determine H2 evolution at the cellular level and to produce new strains with increased ability for H2 production in the two-stage process. [less ▲]

Aphids are some of the most serious pests of cultivated crops worldwide, causing major yield and economic losses. Previous works have demonstrated ants and natural enemies (including ladybeetles and ... [more ▼]

Aphids are some of the most serious pests of cultivated crops worldwide, causing major yield and economic losses. Previous works have demonstrated ants and natural enemies (including ladybeetles and hoverflies) to be able to use aphid volatile chemicals to locate aphid colonies. Here, we report the first isolation of a bacterium from the pea aphid Acyrthosiphon pisum honeydew, Staphylococcus sciuri, which produces kairomones used by the aphidophagous hoverfly Episyrphus balteatus and the Asian Ladybeetle Harmonia axyridis during their search for prey colonies. Some specific semiochemicals produced by S. sciuri were identified as attractants and ovipositional stimulants. Similarly, we have shown scouts of the aphid tending ant species, Lasius niger, to orientate their foraging behaviour toward an Aphis fabae infested plant and we have demonstrated that the odours released by this aphid honeydew were attractive for ant scouts. Again, bacteria were involved in the production of these honeydew semiochemicals. Interestingly, ant scouts were also able to discriminate honeydew odour from A. fabae (usually attended by L. niger) and A. pisum (unattendedby L. niger). Comparison of the volatile and bacteria composition of both aphid species honeydew were attended. [less ▲]

Aphids are one of the most serious pests of crops worldwide, causing major yield and economic losses. To control aphids, natural enemies could be an option but their efficacy is sometimes limited by their ... [more ▼]

Aphids are one of the most serious pests of crops worldwide, causing major yield and economic losses. To control aphids, natural enemies could be an option but their efficacy is sometimes limited by their dispersal in natural environment. Here we report the first isolation of a bacterium from the pea aphid Acyrthosiphon pisum honeydew, Staphylococcus sciuri, which acts as a kairomone enhancing the efficiency of aphid natural enemies. Our findings represent the first case of a host-associated bacterium driving prey location and ovipositional preference for the natural enemy. We show that this bacterium has a key role in tritrophic interactions because it is the direct source of volatiles used to locate prey. Some specific semiochemicals produced by S. sciuri were also identified as significant attractants and ovipositional stimulants. The use of this host-associated bacterium could certainly provide a novel approach to control aphids in field and greenhouse systems. [less ▲]

Aphids are major pests of crops worldwide and the use of pesticides has led to resistant populations. The integration of aphid natural enemies in integrated management programs could be an option, but ... [more ▼]

Aphids are major pests of crops worldwide and the use of pesticides has led to resistant populations. The integration of aphid natural enemies in integrated management programs could be an option, but their efficacy is often limited by their quick dispersal from the ecosystem where they are released. Here, using wind-tunnel and field experiments, we have demonstrated that 3-Methyl-2-butenal acts as an efficient attractant and ovipositional stimulant for the hoverfly Episyrphus balteatus (De Geer) (Diptera: Syrphidae), enhancing its efficiency as biological control agent in crop fields. Wind-tunnel assays allowed determining that a minimal dose of 250 µg of 3-Methyl-2-butenal is required to attract the hoverflies over a distance of 2.5 m while a minimal dose of 500 µg is needed to induce the oviposition. Both attraction and oviposition increased proportionally to the tested doses showing that hoverflies are able to regulate their oviposition according to the chemical stimuli from their environment. In field experiments, both Syrphidae and Chrysopidae were strongly attracted by the 3-Methyl-2-butenal at a dose of 10 mg which also induces the oviposition of these two aphid predators in potato crops. This study also highlighted that hoverflies are the most abundant aphid predators found in natural environment. Against aphids, the use of this semiochemical could certainly enhance the efficiency of natural enemies. Furthermore, the use of the chemical cue 3-Methyl-2-butenal could provide a novel approach to control aphids in field and greenhouse systems. [less ▲]